The present invention relates to a technology of encrypting and decrypting content on a component basis.
In recent years, along with the developments of information communications equipment, various kinds of content have been digitally used. Those kinds of content may include information such as personal information, the viewing of which should be prohibited or restricted depending on users wishing to view the information. For example, if personal information is made public on the Internet, there may be a case where the personal information is abused by a user with malicious intent.
In view of the above, there has been conventionally known a method for protecting content by encrypting the content.
For example, according to the technologies disclosed in Jun Anzai, Natsume Matsuzaki, and Tsutomu Matsumoto, “A Quick Group Key Distribution Scheme with Entity Revocation”, Advances in Cryptology-Asiacrypt'99, Lecture Notes in Computer Science: Vol. 1716 (LNCS1716), pp. 333-347, Springer-Verlag, 1999 (hereinafter referred to as Document 1) and in Nuttapong Attrapadung, Kazukuni Kobara and Hideki Imai, “Broadcast encryption with short keys and transmissions”, Proceedings of the 3rd ACM workshop on Digital rights management, pp. 55-66, 2003 (hereinafter, referred to as Document 2), a method for distributing key information for decrypting encrypted content is devised so as to allow the content to be viewed only by a privileged user in a group.